Abstract The doctrine of divine simplicity says that God is not composed of parts (physical or metaphysical). Modal collapse arguments aim to show that the necessary co-existence of God and creation follows from the doctrine. As noted by Christopher Tomaszewski, R. T. Mullins’s version of this argument assumes that a crucial term occurring within its premises is rigid, leaving the argument invalid or question begging. I examine a recent attempt by Mullins to repair his argument and defend the rigidity of this term. Mullins assumes a test for discerning rigidity on which he and Tomaszewski agree. I argue that this test is false and then provide a new test. My test bodes ill for modal collapse arguments in general.